<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Margin</title>
    <style>
        body {
            margin: 0;
        }

        .first {
            margin: 10px;
            background-color: blue;
        }

        .second {
            margin: 20px;
            background-color: yellow;
        }
    </style>
</head>
<body>
    <p class="first">
        first
    </p>
    <p class="second">second</p>
</body>
</html>